JP5591448B2 - Water absorbing agent and method for producing the same - Google Patents

Description

  The present invention relates to a water absorbing agent and a method for producing the same. More specifically, the present invention relates to a water-absorbing agent preferably used for sanitary materials such as diapers and a method for producing the same.

  Conventionally, water-absorbent resins have a high absorption rate, absorption amount, and retention of aqueous liquids, so in sanitary material applications such as diapers, they are mixed with fiber materials as necessary to constitute sanitary material absorbers. I was trying to do it.

In recent years, with the need for thinning with sanitary materials such as diapers, the ratio of the water-absorbent resin in the absorbent body tends to increase (high concentration) (see, for example, Patent Documents 1 to 3). As the performance of water absorbent resins used in highly concentrated absorbents with high water absorbent resin usage rates, it is known to define the average inter-gap radius between saturated particles under no load and under load. (See Patent Documents 4 and 5). In addition, many water-absorbing resins suitable for use at high concentrations have been proposed (see Patent Documents 6 to 15). However, the water-absorbent resin satisfying the proposed performance has not yet been sufficient in terms of exerting its performance in sanitary materials such as diapers with higher concentrations.
International Publication No. 95/26209 Pamphlet US Pat. No. 5,669,894 US Pat. No. 5,599,335 JP 2003-290290 A US Patent Application Publication No. 2003-0181115 US Pat. No. 5,149,335 US Pat. No. 5,601,542 US Pat. No. 6,414,214 US Pat. No. 6,894,665 US Pat. No. 7,098,284 US Reissue Patent No. 38444 Specification US Pat. No. 5,797,893 US Pat. No. 6,300,305 US Pat. No. 6,831,142 US Pat. No. 6,930,221

  As the proportion of the water-absorbing resin in the absorber increases, as a future water-absorbing resin, a water-absorbing agent that combines the performance of the conventional water-absorbing resin and the performance of the fiber material in the conventional absorber. Development is needed.

  The performance required for such a water-absorbing agent is not only the performance of absorbing and holding an aqueous liquid under no pressure, but also the performance of quickly absorbing an aqueous liquid that has greatly contributed to the performance of the fiber material, There is a performance of diffusing the aqueous liquid after absorbing the aqueous liquid and a performance of holding the aqueous liquid after absorbing the aqueous liquid. In particular, in a highly concentrated absorbent body, the water-absorbent resin after absorbing the aqueous liquid is required to have higher performance because its volume is enlarged and further deformed under pressure.

  The subject of this invention is providing the water-absorbing agent suitable for the hygiene material use provided with the said performance, and other uses.

  As a result of intensive studies to solve the above problems, the present inventor, as a result of absorbing the aqueous liquid under pressure, in the water-absorbing agent essential for the water-absorbent resin particles, the gap diameter between the gel particles under pressure. Has found that it is important to have an unprecedented level, and has found a technique for improving the performance to an unprecedented level, leading to the present invention.

  That is, the water-absorbing agent according to the present invention is a water-absorbing agent essential for water-absorbing resin particles obtained by polymerizing a water-soluble ethylenically unsaturated monomer and having a crosslinked structure therein, and has an average gap radius index under pressure. It is characterized by being 140 or more. However, the average gap radius index under pressure is a value (d50) of the swollen gel gap radius corresponding to 50% of the cumulative gap water amount ratio in physiological saline at a load of 2.07 kPa.

  The water-absorbing agent according to the present invention is a water-absorbing agent obtained by polymerizing a water-soluble ethylenically unsaturated monomer and essentially comprising water-absorbing resin particles having a cross-linked structure therein. The average gap radius index is 100 or more.

  In the water-absorbing agent according to the present invention, the average gap radius index under pressure is a value (d50) of a swollen gel gap radius corresponding to 50% of the cumulative gap water amount ratio in physiological saline at a load of 2.07 kPa. .

  Further, the water-absorbing agent according to the present invention is a water-absorbing agent obtained by polymerizing a water-soluble ethylenically unsaturated monomer and having water-absorbing resin particles having a crosslinked structure inside, and obtained by reverse phase suspension polymerization. 90% by weight or more of the obtained water-absorbing agent has a particle diameter in the range of 150 to 850 μm and contains an average gap radius index improver under pressure.

  The water-absorbing agent may have a particle shape, and 90% by weight (mass)% or more may be particles having a particle diameter of 150 to 850 μm. Further, the absorption capacity under pressure (AAP) at 4.83 kPa can be 10 g / g or more. Further, the surface of the water-absorbent resin particles may be cross-linked, and the water-absorbing agent may include an average gap radius index improver under pressure.

  The water-absorbing agent has a mass average particle diameter (D50) of 200 to 500 μm, a logarithmic standard deviation (σζ) of particle size distribution of 0.25 to 0.45, and a bulk specific gravity (g / ml) of 0.72 to 0.22. It is preferably 1.00.

  Further, the above water-absorbing agent has an absorption capacity under pressure (AAP) at 4.83 kPa of 20 g / g to 29 g / g, the difference between the absorption capacity under load without load (CRC) and the absorption capacity under pressure (AAP) at 4.83 kPa. Is preferably 7 g / g or less.

  In the water-absorbing agent, the water-absorbing resin is preferably spherical and is preferably a granulated product.

  In the method for producing a water-absorbing agent according to the present invention, cross-linking polymerization in which an unsaturated monomer aqueous solution mainly composed of acrylic acid and / or a salt thereof is cross-linked in the presence of an internal cross-linking agent. After the step, the step of adjusting to the water absorbent resin particles satisfying the following (a) to (c) through the drying step, and the treatment for improving the average gap radius index under pressure for the water absorbent resin particles Including the step of applying.

(A) Mass average particle diameter (D50) is 150 to 500 μm, (b) Logarithmic standard deviation (σζ) of particle size distribution is 0.25 to 0.45, and (c) Bulk specific gravity (g / ml) is 0.72. ~ 1.00
Moreover, it is preferable that the said manufacturing method includes the process of bridge | crosslinking the surface of the said water absorbing resin particle after a drying process.

  In addition, the method for producing a water-absorbing agent according to the present invention includes cross-linking polymerization of an unsaturated monomer aqueous solution containing acrylic acid and / or a salt thereof as a main component of a monomer by reverse-phase suspension polymerization in a hydrophobic organic solvent. And a step of adding a surface cross-linking treatment step and an average pore radius index improver under pressure to the obtained water-absorbent resin particles through a drying step.

  In the method for producing a water absorbing agent according to the present invention, the average gap radius index improver under pressure is preferably at least one selected from a polyvalent metal compound, a polycation compound and inorganic fine particles.

  In the method for producing a water-absorbing agent according to the present invention, it is preferable that 90% by weight or more of the water-absorbent resin particles have a particle diameter of 150 to 850 μm.

  In the method for producing a water-absorbing agent according to the present invention, the internal cross-linking agent includes a polymerizable cross-linking agent having two or more polymerizable unsaturated groups, and two or more covalent bond groups or ion bond groups. It is preferable that a reactive internal cross-linking agent is used in combination.

Moreover, in the said manufacturing method of a water absorbing agent, it is preferable that the water absorbing resin at the time of the said surface crosslinking process or after surface crosslinking is adjusted to the water absorbing resin which satisfy | fills following (a)-(c). (A) Mass average particle diameter (D50) is 200 to 500 μm, (b) Logarithmic standard deviation (σζ) of particle size distribution is 0.25 to 0.45, and (c) Bulk specific gravity (g / ml) is 0.72. ~ 1.00
In the method for producing a water-absorbing agent, it is preferable that the average gap radius index improver under pressure contains any polyvalent metal salt from divalent to tetravalent.

  Moreover, the absorbent article for absorption containing the water absorbing agent according to the present invention is an absorbent article for absorbing urine, feces or blood.

  According to the present invention, for example, an absorbent body in a sanitary material such as a diaper is configured to include the water-absorbing agent according to the present invention, so that the water-absorbing agent is a densely structured sandwich core or absorbent body. In the high-concentration core of the water-absorbing agent having a large weight ratio of the absorbent, the aqueous liquid can be diffused in a wider range. In addition, the sanitary material can be reduced in thickness, and thus can play a significant role in sanitary material applications and other applications.

  Hereinafter, the present invention will be described in detail. However, the scope of the present invention is not limited to these descriptions, and modifications other than the following examples can be made as appropriate without departing from the spirit of the present invention.

  In the following description, “weight” is treated as a synonym for “mass”, and “weight%” is treated as a synonym for “mass%”. In addition, “A to B” indicating a range indicates that the range is A or more and B or less.

(Water absorbent resin particles and water absorbent)
The water-absorbing resin particles that can be used in the present invention are water-insoluble water-swellable hydrogel-forming polymers (water-absorbing resin particles) obtained by polymerizing a water-soluble ethylenically unsaturated monomer and having a crosslinked structure inside. The water swellability preferably indicates a water absorption ratio of preferably 10 times or more, and the water insolubility means that the soluble content is preferably 50% by weight (mass) or less, more preferably 20% by weight or less, and further in the range described later. is there. Moreover, the water absorption rate of the physiological saline is at least 10 times. These measurement methods are defined herein.

  Examples of the particle shape include a spherical shape, a shape in which spheres are aggregated, a shape in which the sphere is flattened, an irregularly crushed shape, a shape in which an irregularly crushed product is granulated, and a foamed shape having holes. In the present invention, the water absorbent resin particles may be simply referred to as a water absorbent resin.

  Further, the obtained water-absorbing resin particles may be polished. For polishing the water-absorbent resin particles, for example, a conventionally known polishing apparatus such as a homogenizer exemplified in US Pat. No. 6,562,879 can be used.

  The water-absorbing agent in the present invention refers to an aqueous liquid absorbent solidifying agent containing a water-absorbing resin as a main component, and containing a small amount or a trace amount of additives and water as necessary. In the whole, it is preferably 70 to 100% by weight, more preferably 80 to 100% by weight, still more preferably 90 to 100% by weight. As a small or trace component, water is usually the main component or essential, and further, an average gap radius index improver and additive described below are used.

  The aqueous liquid is not limited to water, but is not particularly limited as long as it includes water, such as urine, blood, feces, waste liquid, moisture and steam, ice, a mixture of water and an organic or inorganic solvent, rainwater, groundwater, Preferably, it is urine, especially human urine, and the water-absorbing agent is an absorption solidifying agent for these.

  Specific examples of water-insoluble water-swellable hydrogel-forming polymers or particles thereof include partially neutralized cross-linked polyacrylic acid polymers (US Pat. No. 462501, US Pat. No. 4,654,039, US Pat. No. 5,250,640, US Pat. No. 5,275,773, European Patent No. 456136, etc.) Cross-linked and partially neutralized starch-acrylic acid graft polymer (US Pat. No. 4,076,663), isobutylene-maleic acid copolymer (US Pat. No. 4,389,513), acetic acid Saponified vinyl-acrylic acid copolymer (US Pat. No. 4,124,748), hydrolyzate of acrylamide (co) polymer (US Pat. No. 3,959,569), hydrolyzate of acrylonitrile polymer (US Pat. No. 3,935,099) Etc.

(Average gap radius index under pressure and its measurement principle)
The average gap radius index under pressure of the present invention represents the diameter of the gap between gel particles under load after the water-absorbent resin (and water-absorbing agent) has absorbed the liquid.

  Conventionally, it has been pointed out that the diameter of the gap between the gel particles is important when the use ratio of the water absorbent resin is high. As a result of intensive studies on the performance of a diaper (leakage reduction, liquid diffusibility) in actual use, the water-absorbent resin (and water-absorbing agent) used in the absorbent material in sanitary materials such as diapers. For the performance of diapers, it was discovered that the diameter of the gap between gel particles under a load corresponding to actual use (average gap radius index under pressure) is particularly important.

  Further, the average gap radius index under pressure of the water-absorbing agent obtained in the present invention is in a range that cannot be obtained by the conventional method. And it discovered that this novel average gap radius index under pressure was achieved by means described later (particle size, polymerization, additives, etc.) which are not disclosed in the above Patent Documents 1-15. Therefore, by using the water-absorbing agent of the present invention in an absorbent body in a sanitary material such as a diaper, the weight ratio of the absorbent core in the absorbent core is a sandwich core that is an absorbent body with a dense structure of the water-absorbing agent. In the high concentration core of many water-absorbing agents, it is possible to diffuse the aqueous liquid to a wider range, reduce urine leakage in actual use, and effectively use the absorber in the diaper. Reduction is possible.

  Hereinafter, the measurement principle of the average gap radius index under pressure will be described.

  The height h at which the liquid ascends the tube of radius R by capillary force is expressed as h = 2γcos θ / ρgR, where γ is the surface tension of the liquid, θ is the contact angle, g is the acceleration of gravity, and ρ is the density of the liquid. (Equation (35) of p428 in P. K. Chatterjee, B. G. Gupta, “TEXTILE SCIENCE AND TECHNOLOGY 13 ABSORBENT TECHNOLOGY 2002” (ELSEVIER)).

  In the apparatus of FIG. 2, by increasing the head difference between the liquid level in the liquid tank and the glass filter of the filter funnel from 0 to h (cm), in the swollen gel and the absorbent body, the gap between the gel particles and the absorbent body Crevice water held at a diameter larger than the capillary radius (gap) of R (μm) among the liquid present in the gas is discharged and escapes. Therefore, the gel which is saturated and swelled and the gap space is completely filled with the liquid is increased from 0 cm in height, and the amount of residual crevice liquid in the gel layer at each predetermined height is measured. The distribution of the gap radius (capillary radius) is obtained.

Hereinafter, in the present invention, the value of the capillary radius R of the sample obtained at each height h using the formula of h = 2γcos θ / ρgR is defined as the gap radius of the sample. The difference between the liquid surface height in the liquid tank and the middle position of the glass filter thickness is 1 cm, 2 cm, 5 cm, 8 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 40 cm, 50 cm, 60 cm from 0 to 60 (cm). By increasing in steps, the liquid held in the gap having the value of R corresponding to each height is discharged. By measuring the amount of discharged liquid, the distribution of the gap radius (capillary radius) of the sample can be calculated, and the value is plotted on logarithmic probability paper, and the value of d50 is taken as the average gap radius. In this example, in the formula h = 2γcos θ / ρgR, γ: surface tension (0.0728 N / m) of physiological saline (0.9 wt% NaCl aqueous solution), θ: contact angle (0 °), ρ: physiological saline The density of water (1000 kg / m ³ ), g: the value of gravity acceleration 9.8 m / s ² shall be used.

  As a result, the liquids held at the positions of 0 cm, 1 cm, 2 cm, 5 cm, 8 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 40 cm, and 50 cm are 1485, 743, 297, 186, 149, 99.0, respectively. It is calculated | required that it is hold | maintained at the clearance gap radius (capillary radius) of 74.3, 59.4, 49.5, 37.1, 29.7, and 24.8 micrometers. In addition, since the measurement in the present invention is performed in a state where the measurement sample sufficiently absorbs the liquid or is wet, θ is set to 0 °.

(Manufacturing method of water-absorbing agent)
Although the manufacturing method of the water absorbing agent of this invention will not be ask | required especially if the physical property of this invention is satisfy | filled, it can obtain by the following <production method 1>, <production method 2>, etc., for example.

<Production method 1 (aqueous solution polymerization)>
When aqueous solution polymerization is used, an unsaturated monomer aqueous solution is subjected to cross-linking polymerization in the presence of an internal cross-linking agent amount within a specific range, and then the obtained hydrogel is pulverized and dried, followed by a sizing step, and specific water absorption. To adjust to the resin particles, and to perform a treatment to improve the average gap radius under pressure. That is, in the aqueous solution polymerization, a surface cross-linking agent and an average gap radius index improver under pressure are used, and the particle diameter and bulk specific gravity may be controlled and adjusted to the water absorption capacity under pressure described later.

<Production Method 2 (Reverse Phase Suspension Polymerization)>
When using reversed-phase suspension polymerization, it is necessary to crosslink the unsaturated monomer aqueous solution in a hydrophobic organic solvent in the presence of a specific range of internal crosslinking agent amount, and then dry the resulting hydrogel. A method of adjusting the specific water-absorbent resin particles through a sizing step, and performing a treatment for improving the average gap radius index under pressure. That is, in the reverse-phase suspension polymerization, a surface cross-linking agent and an average gap radius index improver under pressure are used, and the particle diameter and bulk specific gravity are controlled, and then adjusted to the water absorption capacity under pressure described later.

  In these production methods, the surface of the water-absorbent resin particles is preferably subjected to a crosslinking treatment after drying.

  Hereinafter, the production method of the water-absorbing agent of the present invention and further the water-absorbing agent of the present invention will be described in order. In the following description, it can be used in common for any of the production methods, unless particularly mentioned in Production Method 1 (aqueous solution polymerization), Production Method 2 (reverse phase suspension polymerization) and the beginning of the paragraph.

(monomer)
Examples of the water-soluble ethylenically unsaturated monomer include a carboxyl group-containing water-soluble monomer, a sulfonic acid group-containing water-soluble monomer, an amide group-containing water-soluble monomer, and preferably a carboxyl group-containing water-soluble monomer, particularly preferably Is acrylic acid and / or a salt thereof.

  The water-absorbent resin particles that can be used in the present invention are water-absorbent resin particles made of a polyacrylic acid (salt) -based crosslinked polymer obtained by polymerizing a monomer containing acrylic acid and / or a salt thereof. Is preferred.

  In the present invention, the polyacrylic acid (salt) -based crosslinked polymer preferably contains acrylic acid and / or a salt thereof in an amount of 50 to 100 mol%, more preferably 70 to 100 mol%, and still more preferably 90 to 100 mol%. It is a polymer having a crosslinked structure inside, obtained by polymerizing monomers. The acid group in the polymer is preferably neutralized in an amount of 25 to 100 mol%, more preferably 50 to 99 mol%, and more preferably 55 to 80 mol%. More preferably, examples of the salt include one or more of alkali metal salts such as sodium, potassium and lithium, ammonium salts and amine salts. The neutralization of the acid group for forming the salt may be performed in the monomer state before the polymerization, or may be performed in the polymer state during or after the polymerization, or may be used in combination. Also good.

  As a polyacrylic acid (salt) -based crosslinked polymer preferably used in the present invention as water-absorbent resin particles, in combination with a water-soluble ethylenically unsaturated monomer (acrylic acid and / or salt thereof) used as a main component, If necessary, other monomers may be copolymerized.

  The water-soluble ethylenically unsaturated monomer (acrylic acid and / or salt thereof) is “as the main component” means that the water-soluble ethylenically unsaturated monomer is 70% of the total monomer in the unsaturated monomer aqueous solution. % Or more, preferably 80% or more.

  Specific examples of the other monomers include monomers exemplified in the following US patents and European patents in the polymerization method. Specifically, for example, methacrylic acid, (anhydrous) maleic acid, fumaric acid, Crotonic acid, itaconic acid, vinylsulfonic acid, 2- (meth) acrylamido-2-methylpropanesulfonic acid, (meth) acryloxyalkanesulfonic acid and its alkali metal salts, ammonium salts, N-vinyl-2-pyrrolidone, N -Vinylacetamide, (meth) acrylamide, N-isopropyl (meth) acrylamide, N, N-dimethyl (meth) acrylamide, 2-hydroxyethyl (meth) acrylate, methoxypolyethylene glycol (meth) acrylate, polyethylene glycol (meth) acrylate , Isobutylene, lauryl (meth) a Also include those to be water-soluble or hydrophobic unsaturated monomers body such copolymerizable components such relations. As for the usage-amount of monomers other than these acrylic acid and / or its salt, 0-30 mol% is preferable in all the monomers, More preferably, it is 0-10 mol%.

(Crosslinked structure)
The water absorbent resin particles that can be used in the present invention have a crosslinked structure inside. As a method of introducing an internal cross-linked structure into the water-absorbent resin particles used in the present invention, a method of introducing by self-cross-linking without using a cross-linking agent, two or more polymerizable unsaturated groups and / or two in one molecule Examples thereof include a method of introducing the internal crosslinking agent having the above reactive group by copolymerization or reaction. Specific examples of these internal crosslinking agents include, for example, N, N′-methylenebis (meth) acrylamide, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, trimethylolpropane tri (Meth) acrylate, trimethylolpropane di (meth) acrylate, glycerin tri (meth) acrylate, glycerin acrylate methacrylate, ethylene oxide modified trimethylolpropane tri (meth) acrylate, pentaerythritol tetra (meth) acrylate, dipentaerythritol hexa ( (Meth) acrylate, triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, triallylamine, tetraallyloxyethane, pentaerythritol Copolymerizable crosslinkers such as realyl ether and poly (meth) allyloxyalkane, and internal crosslinkers having a copolymerizable group and a covalent bond group include (poly) ethylene glycol diglycidyl ether, glycerol diglycidyl ether, and ethylenediamine. , Polyethyleneimine, glycidyl (meth) acrylate, hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, glycidyl (meth) acrylate, and the like.

  In addition, as an internal cross-linking agent having two or more covalent bond and ionic bond groups, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, di- Propylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, glycerin, polyglycerin, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol, 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene- Carboxymethyl propylene block copolymer, pentaerythritol, and polyhydric alcohol compounds such as sorbitol, zinc, calcium, magnesium, aluminum, iron, polyvalent metal compound hydroxide or chloride such as zirconium can also be mentioned.

  These internal crosslinking agents may be used alone or in combination of two or more. Especially, the compound which has two or more polymerizable unsaturated groups according to the method described in Japanese Patent Application No. 2005-289399 (international publication 2007/03745 pamphlet) from the water absorption property etc. of the water-absorbing resin obtained. Is preferably used as an internal cross-linking agent. Furthermore, an internal cross-linking agent having a copolymerizable group and a covalent bond group, or an internal cross-linking agent having two or more covalent bond groups or an ionic bond group is used in combination. In particular, it is preferable to use a polyhydric alcohol in combination.

  The amount of the internal crosslinking agent used in the water-absorbent resin particles that can be used in the present invention is 0.005 to 3 mol% with respect to the total monomers (water-soluble ethylenically unsaturated monomers other than the internal crosslinking agent). More preferably, it is 0.01-2 mol%, More preferably, it is 0.2-2 mol%, Most preferably, it is 0.4-1.5 mol%.

  Further, as the internal cross-linking agent in the present invention, (i) an internal cross-linking agent having two or more polymerizable unsaturated groups, (ii) an internal cross-linking agent having a copolymerizable group and a covalent bond group, or a covalent bond When using in combination with an internal cross-linking agent having an internal cross-linking agent having a group or an ion-bonding group, the amount of internal cross-linking agent used is all monomers (water-soluble ethylenically unsaturated monomers other than internal cross-linking agents) Preferably, (i) is 0.005 to 3 mol%, (ii) is 0 to 2.995 mol%, more preferably (i) is 0.01 to 2 mol%, (ii) Is preferably 0 to 1.99 mol%, particularly preferably (i) is 0.2 to 2 mol%, and (ii) is 0 to 1.8 mol%.

  In the polymerization, hydrophilic monomers such as starch or cellulose, starch or cellulose derivatives, polyvinyl alcohol, polyacrylic acid (salt), polyacrylic acid (salt) cross-linked products are all monomers (internal cross-linking). 0 to 30% by weight may be added to water-soluble monomers other than the agent, and chain transfer agents such as hypophosphorous acid (salts) may be added to all monomers (water-soluble monomers other than the internal crosslinking agent). You may add 0 to 1weight% with respect to.

  When the water-absorbing resin obtained by polymerizing in the presence of a water-soluble chain transfer agent in addition to the unsaturated monomer, the internal cross-linking agent, and the polymerization initiator described later is used for the water-absorbing agent of the present invention, the absorption capacity is high. In addition, it is possible to obtain an absorber having excellent stability against urine.

  The water-soluble chain transfer agent is not particularly limited as long as it dissolves in water or a water-soluble ethylenically unsaturated monomer, and includes thiols, thiolic acids, secondary alcohols, amines, hypophosphites and the like. I can list them. Specifically, mercaptoethanol, mercaptopropanol, dodecyl mercaptan, thioglycols, thiomalic acid, 3-mercaptopropionic acid, isopropanol, sodium hypophosphite, formic acid, and salts thereof are selected from these groups One kind or two or more kinds may be used, and it is preferable to use a hypophosphite such as sodium hypophosphite because of its effect. The amount of the water-soluble chain transfer agent used is 0.001 to 1 mol%, preferably 0.005, based on the total amount of monomers, although it depends on the type and amount of the water-soluble chain transfer agent and the concentration of the monomer aqueous solution. -0.3 mol%.

(Polymerization method)
In order to obtain water-absorbing resin particles that can be used in the present invention, the above-described water-soluble ethylenically unsaturated monomer, preferably, a monomer having acrylic acid and / or a salt thereof as a main component is polymerized. Bulk polymerization, reverse phase suspension polymerization, and precipitation polymerization can also be performed. However, from the viewpoint of performance and ease of control of polymerization, it is possible to perform aqueous solution polymerization or reverse phase suspension polymerization using the monomer as an aqueous solution. preferable. In production method 1 of the present application, aqueous solution polymerization is used, and in production method 2, reverse phase suspension polymerization is used.

  Such polymerization methods are described, for example, in US Pat. No. 462501, US Pat. No. 4,769,427, US Pat. No. 4,873,299, US Pat. No. 4,093,763, US Pat. No. 4,367,323, US Pat. U.S. Pat. No. 4,446,261, U.S. Pat. No. 4,683,274, U.S. Pat.No. 4,690,996, U.S. Pat. No. 4,721,647, U.S. Pat. No. 4,738,867, U.S. Pat. It is described in the description.

(Polymerization initiator)
In polymerization, radical polymerization initiators such as potassium persulfate, ammonium persulfate, sodium persulfate, t-butyl hydroperoxide, hydrogen peroxide, 2,2′-azobis (2-amidinopropane) dihydrochloride, ultraviolet rays And active energy rays such as electron beam can be used. Moreover, when using a radical polymerization initiator, it is good also as redox polymerization combining reducing agents, such as sodium sulfite, sodium hydrogensulfite, ferrous sulfate, and L-ascorbic acid. The amount of these polymerization initiators used is preferably 0.001 to 2 mol%, more preferably 0.01 to 0.5 mol%, based on all monomers.

  In carrying out the polymerization, a slurry state exceeding the saturation concentration may be used, but the monomer concentration in the monomer aqueous solution to be used is preferably 35% by weight or more and less than the saturation concentration, and more preferably 37% by weight or more and less than the saturation concentration. More preferred. 0-100 degreeC is preferable and, as for the temperature of monomer aqueous solution, 10-95 degreeC is more preferable. The saturation concentration is defined by the temperature of the monomer aqueous solution.

  Further, the water-absorbent resin particles that can be used in the present invention may be foamed particles. The foamed particles are polymerized by containing an azo-based initiator or a foaming agent such as carbonate, or reverse phase suspension polymerization with O / W / O (oil / water / oil) or inert gas. Expanded particles obtained by polymerizing with bubbles while bubbling.

  The crosslinked polymer obtained by the polymerization is a hydrogel, and the shape thereof is generally an irregularly crushed shape, a spherical shape, a fibrous shape, a rod shape, a substantially spherical shape, a flat shape, or the like.

Hereinafter, reverse phase suspension polymerization in Production Method 2 and gel grinding in Production Method 1 will be described.
(Reverse phase suspension polymerization in production method 2)
In Production Method 2 (Reverse Phase Suspension Polymerization), when the above monomer is polymerized in order to obtain the water-absorbing agent of the invention, the aqueous monomer solution is polymerized in a hydrophobic organic solvent in the presence of a dispersant. Reverse phase suspension polymerization is used in which the polymerization is carried out by dispersion. For example, U.S. Pat. Nos. 4,093,764, 4,340,706, 4,367,323, 4,446,261, 4,683,274, 4,880,888, 5,180,798, 5,244,735, 6,573,330, and U.S. Patent Application No. 2007-015877. And U.S. Patent Application No. 2006-194055. Monomers and initiators exemplified in these polymerization methods can also be used in the present invention.

  Reverse phase suspension polymerization is a polymerization method in which an aqueous monomer solution is suspended or emulsified in a hydrophobic organic solvent, and the monomer is dispersed. Surfactants (US Pat. No. 6,458,896, US Pat. No. 6,107,358) or dispersants for dispersing monomers include, for example, anionic surfactants, nonionic surfactants, cationic surfactants, amphoteric surfactants and the like. It can be illustrated.

  Specifically, anionic surfactants used include mixed fatty acid sodium soap, fatty acid sodium such as sodium stearate, higher alcohol sodium sulfate, sodium alkyl sulfate, alkyl benzene sulfonate, alkyl methyl taurate, polyoxyethylene Examples thereof include alkyl phenyl ether sulfate ester salts, polyoxyethylene alkyl ether sulfonate salts, and sulfosuccinic acid half ester salts of alkyl alcohols. Nonionic surfactants include polyoxyethylene alkyl ethers such as polyoxyethylene higher alcohol ethers, polyoxyethylene alkyl phenyl ethers, sorbitan fatty acid esters, glycerin fatty acid esters, sucrose fatty acid esters, sorbitol fatty acid esters hexaglyceryl monobeherate , Polyalkylene alkyl phenyl ether phosphate ester, polyoxyalkylene alkyl ether phosphate ester, polyoxyalkylene alkyl phenyl ether phosphate ester, polyoxyalkylene aryl ether phosphate ester, and the like. Examples of cationic surfactants and amphoteric surfactants include alkylamines and alkylbetaines. As other dispersants, ethyl cellulose, ethyl hydroxyethyl cellulose, polyethylene oxide, polyethylene-polyacrylic acid copolymer, anhydrous maleated polyethylene, anhydrous maleated polybutadiene, anhydrous maleated EPDM (ethylene-propylene-diene-methylene copolymer) And anhydrous maleated polypropylene. These may be used alone or in combination of two or more.

  Among these surfactants, a nonionic surfactant or anionic surfactant having an HLB (Hydrophile-Lipophile balance) of 2 or more, more preferably 3 or more, such as sorbitan fatty acid ester, sucrose A fatty acid ester or a phosphoric esterified surfactant of an ether type nonionic surfactant is used. Note that the upper limit of HLB is about 16.

  The amount of the surfactant or dispersant used can be appropriately selected depending on the type of polymerization. In general, it is preferably 0.1 to 30 parts by mass, more preferably 0.3 to 5 parts by mass with respect to 100 parts by mass of the whole monomer component composed of a polymerizable monomer and a crosslinkable monomer. Part. The amount of the dispersant or surfactant used is 0.001 to 10% by mass, preferably 0.001 to 1% by mass, based on the organic solvent described later.

  Any organic solvent can be used as the organic solvent used for the reverse phase suspension polymerization as long as it is hardly soluble in water and inert to the polymerization. For example, aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane and n-octane, alicyclic hydrocarbons such as cyclohexane and methylcyclohexane, and aromatic hydrocarbons such as benzene, toluene and xylene Etc. Among these, n-hexane, n-heptane, and cyclohexane can be mentioned as preferred solvents from the viewpoint of industrial availability, quality, and the like. The amount of the hydrophobic solvent used is 0.5 to 10 parts by mass, preferably 0.6 to 5 parts by mass, with respect to 1 part by mass of the polymerizable monomer-containing aqueous solution.

  When producing a water-absorbent resin by reverse phase suspension polymerization, as described above, polymerization is performed using an organic solvent such as n-hexane, n-heptane, cyclohexane, etc., and then surface crosslinking, drying, and granulation are performed. Therefore, the conventional manufacturing method and commercially available products have a problem that a trace amount of organic solvent exists. The water-absorbing agent of the present invention can also be obtained by the manufacturing method according to the present embodiment including this cleaning step.

  In order to reduce the amount of the remaining organic solvent, a method of washing the water-containing gel-like material obtained as described above with an organic solvent or an inorganic solvent having a lower boiling point can be used. As this low-boiling organic solvent, for example, those having a boiling point of 0 ° C. or more and less than 70 ° C., further 30 ° C. or more and less than 50 ° C. are preferable, and among these, acetone, dimethyl ether, methylene chloride and the like are preferable. Specifically, after filtering the hydrogel, it is washed with the low boiling point organic solvent and dried as described above, such as hot air drying. This washing may be performed after the drying process. You may decide to remove an organic solvent at the time of the surface crosslinking process by the high temperature heating mentioned later, without performing this washing | cleaning or using together with this washing | cleaning. The amount of the solvent used for washing is usually 0.5 to 100 parts by mass, preferably 1 to 10 parts by mass, more preferably 2 to 5 parts by mass with respect to 1 part by mass of the water absorbent resin, and the temperature. May be room temperature to boiling point.

(Gel pulverization in production method 1)
In the production method 1 (aqueous solution polymerization), the obtained hydrogel may be dried as it is, but is preferably extruded from a porous structure having a pore diameter of 0.3 to 6.4 mm and pulverized. The shape of the hole is not particularly limited, such as a quadrangle such as a circle, a square, and a rectangle, a triangle, and a hexagon. However, the hole is preferably extruded from a circular hole. In addition, the said hole diameter can be prescribed | regulated by the diameter at the time of converting the outer periphery of an opening part into the outer periphery of a circle | round | yen.

  The pore size of the porous structure for performing extrusion pulverization to obtain pulverized gel particles is more preferably 0.5 to 4.0 mm, and still more preferably 0.5 to 3.0 mm.

  If the pore diameter of the porous structure is smaller than 0.3 mm, the gel may become string-like or the gel may not be extruded. If the pore diameter of the porous structure is larger than 6.4 mm, the effects of the present invention may not be exhibited.

  As an apparatus for performing extrusion pulverization to obtain pulverized gel particles, for example, a hydrated gel polymer is crushed by extruding it from a perforated plate. As an extrusion mechanism, a screw type, a rotating roll type, etc. In addition, a type in which the hydrogel polymer can be pumped from its supply port to the perforated plate is used. The screw-type extruder may be uniaxial or multi-axial, and may normally be used for extrusion molding of meat, rubber and plastic, or may be used as a pulverizer. For example, meat chopper and dome gran are mentioned.

  As described above, a monomer aqueous solution having a specific concentration containing a specific internal crosslinking agent amount is polymerized, and the resulting hydrogel is extruded and pulverized from a porous structure having a specific condition, that is, a pore size of 0.3 to 6.4 mm. To do. In this case, water or a polyhydric alcohol described in the example of the internal cross-linking agent, a mixed solution of water and polyhydric alcohol, a solution in which the polyvalent metal described in the example of the internal cross-linking agent is dissolved in water, or a vapor thereof is added May be.

  The hydrogel obtained by polymerization in production method 1 is preferably dried after passing through a step of obtaining pulverized gel particles by extruding from a porous structure having a pore diameter of 0.3 to 6.4 mm as described above and pulverizing. It is preferable to further pulverize after drying.

  Hereinafter, processes common to the manufacturing methods 1 and 2 will be described again.

(Drying and grinding)
The conditions for drying the hydrogel or crushed gel particles are not particularly limited, but preferably the temperature is 80 to 250 ° C. and the time is 10 to 180 minutes, more preferably the temperature is 150 to 200 ° C. and the time is 30 to 120. For minutes. As a drying method used, for example, a method by azeotropic dehydration in a hydrophobic organic solvent used for polymerization, or after filtering a hydrogel, a normal forced air oven, a vacuum dryer, a microwave dryer, In addition, various methods such as high-humidity drying using high-temperature steam can be adopted so as to achieve a desired moisture content. In the production method 2, azeotropic dehydration can be preferably used. Further, in the production method 2, after the azeotropic dehydration, it can be adjusted so as to have a desired water content by heating at a temperature of 100 ° C. or higher.

  The water content of the water-absorbent resin particles or water-absorbing agent used in the present invention (specified by the amount of water contained in the water-absorbent resin / measured by loss on drying at 180 ° C. for 3 hours) is not particularly limited. In view of the physical properties of the water-absorbing agent, the water-absorbent resin particles preferably exhibit fluidity even at room temperature, and the water content of the water-absorbent resin particles is 0.1 to 30% by mass and 0.2 to 30% by mass. Preferably, it is 0.3-15 mass%, More preferably, it is 0.5-10 mass%.

  By drying, the water-containing gel or pulverized gel particles preferably have a solid content (as defined in the examples) of 70 to 99.8% by weight, more preferably 80 to 99.7% by weight, and still more preferably 90 to 99.99%. 5% by weight. Outside this range, it is difficult to obtain the water-absorbing agent of the present invention.

  The conditions for pulverizing the hydrogel or pulverized gel particles, preferably after drying, are not particularly limited, and conventionally known pulverizers such as a roll mill and a hammer mill can be used.

  The shape obtained by pulverization in Production Method 1 is an irregularly crushed shape. Preferably, it is preferable to grind to a shape close to a sphere. In addition, a spherical shape or a substantially spherical shape obtained by reverse phase suspension polymerization in Production Method 2 without pulverization is also one of the preferred forms.

  Incidentally, as described in JP-A-2001-11106, the particle size can be largely controlled by carrying out the reverse phase suspension polymerization in two stages. Further, as described in WO 2004/083284 pamphlet, post-crosslinking of the water-absorbing resin with a post-crosslinking agent may be performed after completion of the reverse phase suspension polymerization in the final stage, and the final product obtained is The agglomerates may be free from agglomeration of particles, but the agglomerates are preferably as the particle diameter is larger and the amount of the internal crosslinking agent is larger.

(Granulation)
The water-absorbent resin particles that can be used in the present invention may be granulated particles. The granulated particles are granulated particles obtained by granulating particles having a particle size of less than 150 μm. Thus, the method for making at least a part of the water-absorbent resin particles into granulated particles is not particularly limited, and a conventionally known granulation method may be applied.

  As a granulation method, for example, a method in which warm water and fine powder of water absorbent resin particles are mixed and dried (US Pat. No. 6,228,930), or a method in which fine powder of water absorbent resin particles is mixed with an aqueous monomer solution and polymerized (US Pat. 5264495), a method of adding water to fine powder of water-absorbent resin particles and granulating it at a specific surface pressure or higher (European Patent No. 844270), and forming an amorphous gel by sufficiently wetting the fine powder of water-absorbent resin particles And then drying and pulverizing (US Pat. No. 4,950,692), a method of mixing fine particles of water-absorbing resin particles and a polymer gel (US Pat. No. 5,478,879), a method of agglomerating by reverse phase suspension polymerization (US Pat. No. 4,732,968). No.), etc. can be applied.

(Particle size)
The water-absorbent resin particles that can be used in the present invention have a mass average particle diameter of preferably 150 to 500 μm, more preferably 200 to 450 μm, still more preferably 250 to 400 μm, for example, by further classification or granulation. adjust. The logarithmic standard deviation (σζ) is preferably adjusted to 0.25 to 0.45, more preferably 0.25 to 0.40, and still more preferably 0.25 to 0.35. For the water-absorbent resin particles that can be used in the present invention, the effects of the present invention can be further exhibited by adjusting the mass average particle diameter and the logarithmic standard deviation (σζ) in this way.

  In the present invention, when classification is performed as necessary, the sieve used for classification needs to be selected in consideration of classification efficiency. For example, when water-absorbing resin particles, water-absorbing resin particles or water-absorbing agent that have passed through a sieve having an opening of 150 μm are removed by classification operation, it is difficult to completely remove particles having a particle diameter of 150 μm or less. In order to obtain water-absorbing resin particles, water-absorbing resin particles or water-absorbing agent having a particle size of, it is preferable to appropriately select the type of sieve to be used.

  The water-absorbent resin particles that can be used in the present invention preferably include 90 to 100% by weight, and 95 to 100% by weight of particles having a particle diameter of 150 to 850 μm in order to further exert the effects of the present invention. Is more preferable, 98 to 100% by weight is more preferably included, and 99 to 100% by weight is particularly preferable. Further, it is more preferable to contain 90 to 100% by weight of particles having a particle diameter of 150 to 600 μm, and it is particularly preferable to contain 95 to 100% by weight. If there are many particles having a particle diameter of less than 150 μm, the effects of the present invention may not be sufficiently exhibited.

  Furthermore, in order to further demonstrate the effects of the present invention, the content of water absorbent resin particles (specified by sieving classification) in the range of particle diameter of 300 μm or more and 600 μm or less with respect to the total amount of water absorbent resin particles. It is preferable that it is 20-90 mass%, and it is more preferable that it is 50-80 mass%.

  Furthermore, in order to obtain the water-absorbing agent of the present invention, the water-absorbent resin particles in the present invention preferably have a bulk specific gravity (specified in US Pat. No. 6,562,879) in the range of 0.72 to 1.00 g / ml, More preferably, it is in the range of 0.74 to 0.88 g / ml, more preferably in the range of 0.76 to 0.86 g / ml. When the bulk density falls outside the range, the effects of the present invention can be exhibited. It can be difficult.

  Such particle diameter and bulk specific gravity can be obtained, for example, by reverse-phase suspension polymerization with a specific surfactant or by drying / pulverizing after aqueous solution polymerization and further polishing the surface of the resulting particles. In addition, US Pat. No. 5,998,553, US Pat. No. 6,562,879, and US Pat. No. 6,576,713 disclose surface-crosslinked water-absorbing resins having a bulk specific gravity of 0.72 or more. Since the improver is not added or the water absorption capacity under pressure is low, the average gap radius under pressure of the present application is not satisfied.

  Also known are water-absorbing agents (see U.S. Pat. No. 4,507,438 and U.S. Pat. No. 4,541,871) that undergo surface cross-linking after reverse-phase suspension polymerization, because the average gap radius index improver under pressure of the present application is not added. Or, since the water absorption capacity under pressure is low, the average gap radius under pressure of the present application is not satisfied.

  Further, Patent Documents 4 and 5 disclose water-absorbing resins in which the average intergranular radius is controlled, but the methods disclosed in these Patent Documents (control of average particle diameter, addition of cationic polymer and inorganic fine particles) In Reference Examples 1 to 6), it is very difficult or impossible to improve the average gap radius index under pressure according to the present invention. The inventors of the present invention achieved a value exceeding the physical property values disclosed in Patent Documents 4 and 5 by a method not disclosed in Patent Documents 4 and 5, and the novel water-absorbing agent is effective for high-concentration diapers. I found out.

  Hereinafter, the average gap radius index improver under pressure will be described.

(Improvement of average gap radius index under pressure)
In order to obtain the water-absorbing agent of the present invention, it is necessary to subject the water-absorbent resin particles to a treatment for improving the average gap radius index under pressure.

  The treatment for improving the average gap radius index under pressure is not particularly limited, but is preferably performed by adding an agent for improving the average gap radius index under pressure. That is, the water absorbing agent of the present invention preferably contains an average gap radius index improver under pressure.

  In the present invention, the treatment (step) for improving the average gap radius index under pressure may be performed before, simultaneously with, or after the surface treatment (crosslinking) of the water absorbent resin particles described later. Although it is good, in order to exhibit the effect of this invention more, Preferably, it is after surface treatment (crosslinking), and it is preferable to carry out separately from surface treatment (crosslinking).

  As an average gap radius index improver under pressure, a compound selected from polyvalent metal compounds, inorganic fine particles, polycationic polymer compounds, water-soluble polyvalent metal salts, water-insoluble inorganic fine particles, polyamine polymer compounds (weight) A compound selected from an average molecular weight of 1000 or more, and further 10,000 to 1,000,000) can be used, and an average gap radius index improver under inorganic pressure, particularly a water-soluble polyvalent metal salt is particularly preferable.

  For example, polyvalent metal compounds such as ammonium zirconium carbonate, aluminum sulfate, potassium alum, ammonium alum, sodium alum, (poly) aluminum chloride, and their hydrates; polycation polymers such as polyethyleneimine, polyvinylamine, and polyallylamine Compounds; water-insoluble inorganic fine particles such as silica, alumina, bentonite; and the like. These may be used alone or in combination of two or more. Among these, water-soluble polyvalent metal salts (particularly aluminum salts) such as aluminum sulfate and potassium alum are preferable in terms of improving the average gap radius index under pressure. The valence of the polyvalent metal salt is preferably any of divalent to tetravalent.

  The average gap radius index improver under pressure is preferably used in a proportion of 0.001 to 10% by weight with respect to the water-absorbent resin particles, 0.01 to 5% by weight, and further 0.05 to 3% by weight. In particular, it is more preferable to use at a ratio of 0.08 to 2% by weight. When the polyvalent metal salt is a hydrate (eg, aluminum sulfate 16 hydrate), the weight includes water molecules. Further, the amount of addition depends on the particle diameter (surface area) of the water-absorbent resin particles. When the surface area relative to the volume of the water-absorbent resin is large (when the particle diameter of the water-absorbent resin is small), the average gap under pressure When the surface area with respect to the volume of the water absorbent resin is narrow (when the particle diameter of the water absorbent resin is large), the addition amount of the radius index improver is small. Further, the amount of the average gap radius index improver under pressure depends on the gel strength after liquid absorption of the water-absorbent resin particles, and when the gel strength is high, the amount of the average gap radius index improver under pressure is If the gel strength is low, a large amount of the average gap radius index improver under pressure is required.

  The addition method of the average gap radius index improver under pressure is not particularly limited, and may be dry blend, added as an aqueous solution, or a method by heat fusion.

  More specifically, dry blending is a method of uniformly mixing the above-mentioned average gap radius index improver under pressure, such as a solid and powdery polyvalent metal compound or inorganic fine particles, into dry-pulverized water-absorbent resin particles. It is a method, and if necessary, after mixing, water or an aqueous solution of a polyhydric alcohol may be further added and mixed, or may be further heated. The aqueous solution addition is a method of adding and mixing an aqueous solution of a polyvalent metal compound or polycation compound to the water-absorbent resin particles, and it is preferable that the concentration of the polyvalent metal compound or polycation compound is higher. Moreover, you may heat after mixing as needed. Thermal fusion refers to a mixture of polyvalent metal hydrates such as aluminum sulfate, potassium alum, ammonium alum, and sodium alum and water-absorbent resin particles simultaneously with or after mixing, and then heating or pre-heated water-absorbent resin particles. In this method, the polyvalent metal hydrate is melted and mixed with the water-absorbent resin particles by mixing the polyvalent metal compound. If necessary, water may be added before heating.

(Surface cross-linking)
The water-absorbent resin particles that can be used in the present invention are preferably those whose surfaces are crosslinked in order to further exhibit the effects of the present invention.

  The step of cross-linking the surface of the water-absorbent resin particles to obtain the water-absorbent resin particles can be performed at least one selected from before, simultaneously with, and after the step of improving the average gap radius under pressure. preferable.

  Examples of the surface cross-linking agent that can be used for the surface cross-linking treatment include organic surface cross-linking agents, polyvalent metal compounds, and polycations having two or more functional groups that can react with the water-absorbent resin particles, in particular, carboxyl groups. These are preferably used in combination. Among these surface cross-linking agents, an organic surface cross-linking agent is used in order to obtain the water-absorbing agent of the present application. In this case, the above-mentioned average gap radius index improver under pressure (in particular, the average gap radius index improver under inorganic pressure, A polyvalent metal salt) is used or used in combination.

  For example, ethylene glycol, diethylene glycol, propylene glycol, triethylene glycol, tetraethylene glycol, polyethylene glycol, 1,3-propanediol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polypropylene glycol, Glycerin, polyglycerol, 2-butene-1,4-diol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,2-cyclohexanedimethanol 1,2-cyclohexanol, trimethylolpropane, diethanolamine, triethanolamine, polyoxypropylene, oxyethylene-oxypropylene block copolymer, pentaerythritol, sorbitol Polyhydric alcohol compounds such as ethylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, glycerol polyglycidyl ether, diglycerol polyglycidyl ether, polyglycerol polyglycidyl ether, propylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycidol, etc. Epoxy compounds; polyvalent amine compounds such as ethylenediamine, diethylenetriamine, triethylenetetramine, tetraethylenepentamine, pentaethylenehexamine, and polyethyleneimine, and inorganic or organic salts thereof (for example, azetidinium salts); 2,4-tri Polyisocyanate compounds such as range isocyanate and hexamethylene diisocyanate; 1,2-ethyl Multivalent oxazoline compounds such as bis-oxazoline; carbonic acid derivatives such as urea, thiourea, guanidine, dicyandiamide, 2-oxazolidinone; 1,3-dioxolan-2-one, 4-methyl-1,3-dioxolan-2-one 4,5-dimethyl-1,3-dioxolan-2-one, 4,4-dimethyl-1,3-dioxolan-2-one, 4-ethyl-1,3-dioxolan-2-one, 4-hydroxy Methyl-1,3-dioxolan-2-one, 1,3-dioxan-2-one, 4-methyl-1,3-dioxan-2-one, 4,6-dimethyl-1,3-dioxane-2- Alkylene carbonate compounds such as ON; haloepoxy compounds such as epichlorohydrin, epibromohydrin, α-methylepichlorohydrin, and polyvalent amides thereof; Adducts (for example, Kaymen manufactured by Hercules: registered trademark); Silane coupling agents such as γ-glycidoxypropyltrimethoxysilane, γ-aminopropyltriethoxysilane; 3-methyl-3-oxetanemethanol, 3-ethyl-3 -Oxetanemethanol, 3-butyl-3-oxetanemethanol, 3-methyl-3-oxetaneethanol, 3-ethyl-3-oxetaneethanol, 3-butyl-3-oxetaneethanol, 3-chloromethyl-3-methyloxetane, Examples thereof include oxetane compounds such as 3-chloromethyl-3-ethyloxetane and polyvalent oxetane compounds; hydroxides such as zinc, calcium, magnesium, aluminum, iron and zirconium, and polyvalent metal compounds such as chlorides.

  These surface cross-linking agents may be used alone or in combination of two or more. Of these, polyhydric alcohols are preferred because they are highly safe and can improve the hydrophilicity of the surface of the water-absorbent resin particles. In addition, the use of polyhydric alcohol improves the familiarity with the polyvalent metal particles on the surface of the water-absorbent resin particles. It becomes possible to make a valence metal particle exist more uniformly.

  As for the usage-amount of a surface crosslinking agent, 0.001-5 weight part is preferable with respect to 100 weight part (mass part) of solid content of a water absorbing resin particle.

  Water may be used in mixing the surface cross-linking agent and the water-absorbent resin particles. The amount of water used is preferably more than 0.5 and not more than 10 parts by weight, more preferably in the range of 1 to 5 parts by weight, based on 100 parts by weight of the solid content of the water-absorbent resin.

  When mixing the surface crosslinking agent or an aqueous solution thereof, a hydrophilic organic solvent exemplified in US Pat. No. 5,610,208 or a third substance may be used as a mixing aid. The amount of the hydrophilic organic solvent used is preferably 10 parts by weight or less with respect to 100 parts by weight of the solid content of the water-absorbent resin particles, although it depends on the type, particle size, water content and the like of the water-absorbent resin particles. More preferably within the range of ˜5 parts by weight. In addition, inorganic acids, organic acids, polyamino acids and the like shown in US Pat. No. 5,610,208 may be present as the third substance. These mixing aids may act as a surface cross-linking agent, but those that do not deteriorate the water absorption performance of the water-absorbent resin particles after the surface cross-linking are preferable. In particular, volatile alcohols having a boiling point of less than 150 ° C. are volatilized during the surface cross-linking treatment, and therefore it is desirable that no residue remains.

  The mixing method for mixing the water-absorbent resin particles and the surface cross-linking agent is not particularly limited. For example, the water-absorbent resin particles are immersed in a hydrophilic organic solvent and dissolved in water and / or the hydrophilic organic solvent as necessary. Examples thereof include a method of mixing a surface cross-linking agent and a method of directly mixing water-absorbent resin particles with a surface cross-linking agent dissolved in water and / or a hydrophilic organic solvent by spraying or dropping. Moreover, when spraying a surface crosslinking agent solution, it is preferable that the magnitude | size of the sprayed droplet is 1-300 micrometers, and it is more preferable that it is 2-200 micrometers.

  After mixing the water-absorbent resin particles and the surface cross-linking agent, usually, heat treatment is preferably performed to carry out the cross-linking reaction. Although the said heat processing temperature is based also on the surface crosslinking agent to be used, 40 to 250 degreeC is preferable and 150 to 250 degreeC is more preferable. When the treatment temperature is less than 40 ° C., the absorption characteristics such as the absorption capacity under pressure may not be sufficiently improved. When the treatment temperature exceeds 250 ° C., the water-absorbent resin particles are deteriorated and the performance may be deteriorated. The heat treatment time is preferably 1 minute to 2 hours, more preferably 5 minutes to 1 hour. By increasing the water absorption capacity under pressure to a predetermined range by such surface crosslinking with a specific particle size, the average gap radius index under pressure can be improved.

(Physical properties of water-absorbing agent)
The water-absorbing agent of the present invention taking the above production method as an example provides a novel water-absorbing agent.

  That is, the first water-absorbing agent of the present invention is a water-absorbing agent essential for water-absorbing resin particles obtained by polymerizing a water-soluble ethylenically unsaturated monomer and having a crosslinked structure therein, and the average gap radius under pressure It is a novel water absorbing agent having an index of 140 or more.

  Further, the second water-absorbing agent of the present invention is a water-absorbing agent essential for water-absorbing resin particles obtained by polymerizing a water-soluble ethylenically unsaturated monomer and having a crosslinked structure therein, and is 90 wt. % Or more is a water absorbing agent having a particle diameter in the range of 150 to 850 μm and an average gap radius index under pressure of 100 or more.

  Further, the third water-absorbing agent of the present invention is a water-absorbing agent obtained by polymerizing a water-soluble ethylenically unsaturated monomer and having water-absorbing resin particles having a crosslinked structure therein, and is a reverse phase suspension polymerization. 90% by weight or more of the water-absorbing agent obtained in the above is a water-absorbing agent having a particle diameter in the range of 150 to 850 μm and containing an average gap radius index improver under pressure. It is preferably surface-crosslinked, exhibits the above-mentioned average gap radius index improver under pressure and other physical properties, and has a spherical shape. The water absorbing agent is preferably a granulated product. The third water-absorbing agent can suitably improve the average gap radius index under pressure while maintaining other physical properties such as CRC and AAP high.

  Hereinafter, the physical properties of the water-absorbing agent of the present invention will be described.

(A) Average gap radius index under pressure The water-absorbing agent of the present invention is characterized by a high average gap radius index under pressure. The average gap radius index under pressure is essentially 100 or more, preferably 120 or more, more preferably 140. More preferably, it is 150 or more, still more preferably 160 or more, still more preferably 170 or more, particularly preferably 200 or more, and most preferably 300 or more. Although an upper limit is not specifically limited, Preferably it is 1000 or less, More preferably, it is 800 or less. If it is smaller than 140, for example, urine is less likely to be diffused in the absorbent body and may leak. On the other hand, if it exceeds 1000, there is a possibility that the diffusion of the liquid is too good and leakage occurs.

  For the above reasons, the water-absorbing agent according to the present invention has a gap distribution index under pressure (logarithmic average standard deviation (σζ)) of 0.2 to 1.5, preferably 0.4 to 1.4.

(B) Shape The shape of the water-absorbing agent according to the present invention is not particularly limited as long as it satisfies the above physical properties, and examples thereof include a sheet shape and a fiber shape, and particularly preferably a particulate shape or a spherical shape. From the balance of physical properties, the water-absorbing agent is preferably a granulated product (for example, a granulated product of spherical particles).

  When the water-absorbing agent used in the present invention is in the form of particles, the particle diameter and particle size distribution of the water-absorbing agent are not particularly limited, but in order to further exert the effects of the present invention, the mass average particle diameter is preferably 150 to It is 850 micrometers, More preferably, it is 200-600 micrometers, More preferably, it is 250-500 micrometers. The logarithmic standard deviation (σζ) is preferably 0.45 to 0.20, more preferably 0.35 to 0.22, and still more preferably 0.30 to 0.25. Moreover, it is preferable that a mass average particle diameter contains 300-600 micrometers particle | grains, The ratio (specified by sieve classification) becomes like this. Preferably it is 20 to 90 weight%, More preferably, it is 50 to 80 weight%. The bulk specific gravity is 0.72 to 1.00 g / ml, more preferably 0.74 to 0.88 g / ml, and still more preferably 0.76 to 0.86 g / ml. When it comes off, it may be difficult to exert the effect of the present invention.

  In the case of a particulate water-absorbing agent, the water-absorbing agent according to the present invention preferably includes 90 to 100% by weight of particles having a particle size of 150 to 850 μm on a standard sieve in order to further exert the effects of the present invention. It is more preferable to contain 95 to 100% by weight, 98 to 100% by weight, and 99 to 100% by weight. If there are many particles having a particle diameter of less than 150 μm, the liquid permeability may deteriorate and the effects of the present invention may not be sufficiently exhibited. If there are many particles having a particle size larger than 850 μm, for example, gel particles may move rapidly after absorption, and the shape of the absorber may collapse, resulting in urine leakage from the diaper and unpleasantness to the human body. is there.

(B) Absorption capacity without load (CRC)
The water-absorbing agent of the present invention has an unloaded water absorption capacity (CRC) of 10 g / g or more, more preferably 15 to 60 g / g, still more preferably 20 to 40 g / g, and particularly preferably 25 to 35 g / g. When the water absorption ratio (CRC) is smaller than 10 g / g, the amount of the water-absorbing agent used increases, and for example, the diaper becomes thick. If the water absorption ratio (CRC) is larger than 60 g / g, the liquid diffusibility after absorption may be poor.

(C) Absorption capacity under pressure (AAP)
The water-absorbing agent of the present invention has an absorption capacity under load (AAP) at 4.83 kPa of preferably 10 to 30 g / g, more preferably 15 to 30 g / g, 20 g / g to 29 g / g, and 22 to 28 g / g. . When the absorption capacity under pressure (AAP) is smaller than 10 g / g, the amount of the water-absorbing agent used increases, and for example, the diaper becomes thick.

(D) Difference between absorption capacity under pressure (AAP) at 4.83 kPa and water absorption capacity (CRC) under no load The water absorption agent of the present invention has an absorption capacity under pressure (AAP) at 4.83 kPa and water absorption capacity under load (CRC). ) Is 7 g / g or less, preferably 6 g / g or less, more preferably 5 g / g or less. When the difference between the absorption capacity under pressure (AAP) at 4.83 kPa and the water absorption capacity under load (CRC) exceeds 7 g / g, the liquid diffusibility under pressure may be inferior. The lower limit may be negative (eg, about -3, or about -1), but is usually zero. (A) to (d) are appropriately obtained by adjusting internal cross-linking and surface cross-linking by the above method).

(E) Absorption rate (FSR)
The water-absorbing agent of the present invention has an absorption rate (FSR) with respect to 20 times physiological saline of 0.05 g / g / s or more, preferably 0.1 g / g / s or more, more preferably 0.2 g / g / s. More preferably, it is 0.3 g / g / s or more, still more preferably 0.5 g / g / s or more, and particularly preferably 0.7 g / g / s or more. Although an upper limit is not specifically limited, Preferably it is 10 g / g / s or less, More preferably, it is 5 g / g / s or less. If the absorption rate (FSR) is smaller than 0.2 g / g / s, for example, when used for a diaper, urine may leak without being sufficiently absorbed. Such FSR can be improved by foaming or granulation.

(F) Soluble content The water-absorbing agent of the present invention preferably has a soluble content of 0 to 15 wt%, more preferably 0 to 10 wt%, and even more preferably 0 to 8 wt%. If the soluble content is more than 15% by weight, for example, when using a diaper or the like, there is a risk of becoming slimy. The soluble amount can be controlled by the polymerization temperature, concentration, amount of crosslinking agent, and the like.

(G) Components other than the water absorbent resin The water absorbent according to the present invention includes the water absorbent resin particles described above. When the water-absorbing agent according to the present invention includes water-absorbing resin particles that have not been subjected to a treatment for improving the average gap radius index under pressure, the water-absorbing agent further includes an average gap radius index improver under pressure at the above-mentioned content ratio. It is preferable. When the water-absorbing agent according to the present invention includes water-absorbing resin particles that have been subjected to treatment for improving the average gap radius index under pressure, the water-absorbing agent according to the present invention may be composed of only the water-absorbing resin particles.

  Further, the water-absorbing agent according to the present invention includes a deodorant (eg, exemplified in US Pat. No. 6,469,080), an antibacterial agent, a reducing agent (eg, exemplified in US Pat. No. 4,959,060), a surfactant, an antioxidant, and an oxidizing agent. A chelating agent (for example, US Pat. No. 6,599,989) is preferably contained in the range of 0 to 10% by weight, more preferably 0.001 to 5% by weight, and 0.05 to 3% by weight with respect to the water-absorbent resin particles. You may go out. When the surfactant is contained in the above amount with respect to the water-absorbing agent, it is possible to suppress deterioration of physical properties during transportation or storage. Further, the water-absorbing agent according to the present invention has a predetermined amount of water, preferably 0.1 to 15% by weight, more preferably 0.5 to 10% by weight, and particularly 0.8 to 9% by weight from the viewpoint of water absorption speed and impact resistance. % Is preferable. Chelating agents and reducing agents are suitable for urinary resistance and coloration prevention.

(Use)
The water-absorbing agent according to the present invention is suitably used for applications such as sanitary materials such as diapers, water-absorbing agents for simple toilets, solidifying agents for waste liquids, and water retention agents for agriculture, and is particularly suitable for sanitary materials such as diapers.

  The absorbent article of the present invention is for absorption of urine, preferably feces or blood, and has an absorbent body obtained by molding a particulate water-absorbing agent and, if necessary, hydrophilic fibers into a sheet shape, and has liquid permeability An absorbent article comprising a top sheet and a back sheet having liquid impermeability. When the hydrophilic fiber is not used, the absorbent body is configured by fixing a particulate water-absorbing agent to paper and / or nonwoven fabric. In the case of using a fiber material (pulp), a fiber base material that can be used by being sandwiched or blended, and can be used as pulverized wood pulp, cotton linter and crosslinked cellulose fiber, rayon, cotton, wool, acetate, Examples thereof include hydrophilic fibers such as vinylon, and those obtained by airlaid are preferable.

  The content (core concentration) of the particulate water-absorbing agent in the absorbent body in the absorbent article is 30 to 100% by mass, preferably 40 to 100% by mass, more preferably 50 to 100% by mass, and still more preferably 60 to 60%. The effect of the present invention is exhibited at 100% by mass, particularly preferably 70 to 100% by mass, and most preferably 75 to 95% by mass. For example, when the particulate water-absorbing agent of the present invention is used at the above-mentioned concentration, particularly in the upper layer portion of the absorber, because of its high liquid permeability (liquid permeability under pressure), it is excellent in diffusibility of the absorbing liquid such as urine, Absorbent articles such as disposable diapers can be provided with an absorbent article that maintains the hygienic white state in addition to improving the amount of absorption of the entire absorbent article by efficient liquid distribution.

The absorber is preferably compression-molded so that the density is 0.06 g / cc or more and 0.50 g / cc or less, and the basis weight is 0.01 g / cm ² or more and 0.20 g / cm ² or less.

  Hereinafter, although an example and a comparative example explain the present invention still in detail, the present invention is not limited to these examples.

  Various performances of the water-absorbing agent (or water-absorbing resin particles) were measured by the following methods.

  All electric devices used in the measurement were used under the conditions of 200 V or 100 V, 60 Hz, and measured under the conditions of 25 ° C. ± 2 ° C. and relative humidity of 50% RH. Moreover, 0.90 mass% sodium chloride aqueous solution was used as physiological saline. The reagents and instruments exemplified in the following measurement methods and examples may be appropriately replaced with equivalents.

<(A) Average gap radius index under pressure>
Using the measuring apparatus shown in FIG. 2, the interstitial gap index under no pressure at the time of saturation swelling of the water-absorbent particles or the water-absorbent particles was measured in the following steps.

≪Step (1) ≫
A filter funnel 201 (glass filter particle number # 3; having a thickness of 5 mm, an average pore diameter of about 20 to 30 μm and having a height difference of 60 cm and no introduction of air) having a liquid absorption surface of 60 mm in diameter A conduit 203 is connected to the lower part of the glass filter 202, and this conduit 203 is connected to a port provided at the lower part of a liquid tank 204 having a diameter of 10 cm. At this time, the glass filter 202 must be sufficiently adjusted so that no air remains. The filter funnel 201 is fixed by a clamp 205 so that the glass filter 202 is horizontal. The filter funnel 201 and its lower part and conduit 203 are filled with physiological saline (0.9 wt% sodium chloride aqueous solution) 206. The liquid tank 204 is placed on the balance 207, and the balance 207 is connected to the computer 210, and the change in the liquid mass in the liquid tank 204 can be recorded in the computer.

  The filter funnel 201 fixed by the clamp 205 can automatically raise and lower the glass filter to each height by an automatic elevator 208 according to a preset program. In this case, the ascending / descending speed is 1.0 cm / sec. After confirming that there is no air in the conduit and in the lower part of the glass filter of the filter funnel, the liquid level at the upper part of the physiological saline 206 in the liquid tank 204 is matched with the intermediate position level of the thickness of the glass filter 202 (high 0 cm).

  Next, the filter funnel is raised, and the difference between the intermediate position level of the thickness of the glass filter 202 and the liquid surface level above the physiological saline 206 is set to 60 cm, and the balance value is set to zero. The height of the filter funnel 201 is based on the position (height 0 cm) where the liquid level at the top of the physiological saline 206 in the liquid tank 204 and the intermediate position level of the thickness of the glass filter 202 are matched. A difference between the height of 0 cm and the height of the intermediate position level of the thickness of the glass filter 202 is taken as a difference.

≪Step (2) ≫
After recording the liquid mass by the computer 210, the measurement sample 209 (water absorbent or water absorbent resin particles) is placed on the glass filter 202 under the following conditions, and the acrylic resin piston 211 is placed on the measurement sample 209. A weight 212 having a hole penetrating vertically with a diameter of 15 mm is installed at the center. The total pressure of the piston 211 and the weight 212 is adjusted to 2.07 kPa. The piston 211 has an outer diameter slightly smaller than 60 mm, there is almost no gap between it and the inner wall surface of the filter funnel 201, and vertical movement is not hindered. Further, the piston 211 has a height of 3 cm, and has a hole penetrating vertically as shown in FIG. 3, and a stainless steel 400 mesh wire mesh is fused to the bottom.

(When measurement sample 209 is a particle)
Water-absorbing agent particles 0.900 g or water-absorbing agent particles 0.900 g (W) sieved to 600 to 300 μm are sprayed uniformly and quickly on the glass filter 202.

(When measurement sample 209 is not in a particle shape)
A sample prepared by punching into a circle with a diameter of 57 mm is placed on the glass filter 202 after measuring the weight (W) in a dry state.

  In addition, the state which does not have the measurement sample 209 on the glass filter 202, ie, a blank, is measured similarly to the below-mentioned.

≪Step (3) ≫
The difference between the glass filter 202 thickness and the intermediate position level height is set to -3 cm (the position where the glass filter 202 is lower), and the sample is swollen until the liquid mass change is less than 0.005 g / min (for example, 30 minutes). Let At this time, the sample is completely immersed in physiological saline so that there is no air bubble.

≪Step (4) ≫
The height of the glass filter 202 is maintained until the difference between the thickness of the glass filter 202 and the height at the intermediate position is 0 cm, and the liquid mass change is less than 0.005 g / min (for example, 60 minutes). The value (g) of the balance when it becomes less than 0.005 g / min is defined as A0.

≪Step (5) ≫
Similarly, the difference (cm) of the thickness of the glass filter 202 from the intermediate position level height is increased to 0, 1, 2, 5, 8, 10, 15, 20, 25, 30, 40, 50, 60 cm, respectively. The value (g) of the balance when the liquid mass change is less than 0.005 g / min is A0, A1, A2, A5, A8, A10, A15, A20, A25, A30, A40, A50, A60. .

≪Step (6) ≫
In the state where there is no sample on the glass filter (blank), the difference (cm) between the thickness of the glass filter 202 and the intermediate position level height is 0, 1, 2, 5, 8, 10 with no piston and weight. , 12, 20, 25, 30, 40, 60 cm, and the values (g) of the balance when the liquid mass change becomes less than 0.005 g / min, respectively, are B0, B1, B2, B5, B8, Let B10, B12, B20, B25, B30, B40, B50, B60.

≪Step (7) ≫
In the present invention, as a value reference of (A60-B60), a value obtained by subtracting (A60-B60) from the liquid mass (for example, A30-B30) at each height (the actual balance value is negative, Let the absolute value cm be 0 cm, 1 cm, 2 cm, 5 cm, 8 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 40 cm, 50 cm, 60 cm.

≪Step (8) ≫
Next, the ratio of the accumulated crevice water amount is calculated from the crevice water amount at each height. As described above, the liquids held at the positions of 0 cm, 1 cm, 2 cm, 5 cm, 8 cm, 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 40 cm, and 50 cm are 1485, 743, 297, 186, 149, and 99.0, respectively. , 74.3, 59.4, 49.5, 37.1, 29.7, 24.8 μm gap radius (capillary radius), and the liquid held at 60 cm is 24.8 μm gap. When passing through the radius (capillary radius), the value of the capillary radius is plotted on a logarithmic probability paper with respect to the cumulative gap water amount at each height.

  The value (d50) of the gap radius corresponding to 50% of the cumulative gap water amount ratio in this graph is determined and used as the average gap radius index (μm) under pressure of the sample. In addition, the logarithmic standard deviation (σζ) of the distribution is obtained from the following formula from the cumulative crevice water amount ratio at each height.

Gap distribution index under pressure σζ = 0.5 × ln (X2 / X1)
(X1 is R = 84.1%, X2 is the gap radius when R = 15.9%)
However, the height (0 cm to 50 cm) directly indicating 84.1% and 15.9% may be appropriately adjusted without plotting on logarithmic probability paper.

≪Step (9) ≫
Further, when the average gap radius index (μm) under pressure was determined by this method using spherical glass beads of 350 to 500 μm and 1000 to 1180 μm as standard samples in order to confirm the measured values, 86 (μm) and 217 (μm) were obtained, respectively. ) Was asked.

<(B) Shape-logarithmic standard deviation of particle size distribution (σζ)>
The water-absorbing agent (or water-absorbing resin particles) is sieved with JIS standard sieves (JIS Z8801-1 (2000)) having openings of 850 μm, 710 μm, 600 μm, 500 μm, 425 μm, 300 μm, 212 μm, 150 μm, 45 μm, and the residual percentage R Were plotted on log-probability paper.

  When a water-absorbing resin exceeding 850 μm is included, a JIS standard sieve having a commercially available mesh exceeding 850 μm is used as appropriate. Therefore, when X1 is R = 84.1% by weight and X2 is each particle size when 15.9% by weight, the logarithmic standard deviation (σζ) is expressed by the following formula, and the smaller the value of σζ, the smaller the particle size. Means a narrow distribution.

σζ = 0.5 × ln (X2 / X1)
The classification method for measuring the logarithmic standard deviation (σζ) in the particle size and particle size distribution is as follows. 10.0 g of water-absorbing resin particles or water-absorbing agent is charged into the JIS standard sieve (THE IIDA TESTING SIEVE: diameter 8 cm), and vibration classification is performed. Classification was carried out for 5 minutes using a vessel (IIDA SIEVE SHAKER, TYPE: ES-65 type, SER. No. 0501).

<(B) Shape-Mass average particle diameter (D50)>
The water-absorbing agent (or water-absorbing resin particles) was sieved with the JIS standard sieve, and the residual percentage R was plotted on a logarithmic probability paper. Thereby, the mass average particle diameter (D50) was read.

<(C) Absorption capacity without pressure (CRC: Centrifuged retention capacity)>
The water-absorbing agent (or water-absorbing resin particles) W (g) (about 0.20 g) obtained in Examples and Comparative Examples to be described later is put into a non-woven bag (60 mm × 85 mm, material is EDANA ERT 441.1-99). And was immersed in 0.90% by mass physiological saline adjusted to 25 ± 2 ° C. After 30 minutes, the bag was pulled up, drained at 250 G (250 × 9.81 m / s ² ) for 3 minutes using a centrifuge (manufactured by Kokusan Co., Ltd., model H-122 small centrifuge), Mass W2 (g) was measured. Moreover, the same operation was performed without using a water absorbing agent (or water absorbing resin particles), and the mass W1 (g) at that time was measured. And CRC (g / g) was computed from the said mass W, W1, W2 according to following Formula.

CRC (g / g) = {(mass W2 (g) −mass W1 (g)) / W (g)} − 1
<(D) Absorbency against Pressure (AAP)>
Absorbency against pressure (AAP)
The absorption capacity under pressure (AAP) represents the absorption capacity under pressure at 4.83 kPa for 60 minutes with respect to physiological saline (0.9 wt% sodium chloride aqueous solution).

  It measured using the apparatus shown in FIG.

  A stainless steel 400 mesh wire mesh (mesh size 38 μm) 101 was fused to the bottom of a plastic support cylinder 100 having an inner diameter of 60 mm. Under conditions of room temperature (23.0 ± 2.0 ° C.) and humidity of 50 RH%, 0.90 g of the water absorbent resin (102) was uniformly sprayed on the wire mesh, and 4 wt. The piston 103 and the load 104 that were adjusted so that a load of .83 kPa (0.7 psi) could be applied uniformly were placed in this order, and the weight Wa (g) of this measuring device set was measured. The piston 103 has an outer diameter slightly smaller than 60 mm, there is almost no gap between the piston 103 and the inner wall surface of the support cylinder, and the vertical movement is not hindered.

  A glass filter 106 (manufactured by Mutual Riken Glass Co., Ltd., pore diameter: 100-120 μm) having a diameter of 90 mm and a thickness of 5 mm is placed inside a petri dish 105 having a diameter of 150 mm, and physiological saline (0.9 wt% sodium chloride) Aqueous solution) 108 (20 to 25 ° C.) was added so as to be at the same level as the upper surface of the glass filter. On top of that, a sheet of filter paper (107) with a diameter of 90 mm (ADVANTEC Toyo Co., Ltd., product name: (JIS P 3801, No. 2), thickness 0.26 mm, retained particle diameter 5 μm) is placed so that the entire surface gets wet. And excess liquid was removed.

  On the moist filter paper, the set of measuring devices was placed, and the liquid was absorbed under load for a predetermined time. This absorption time was calculated from the start of measurement and was 1 hour later. Specifically, after 1 hour, the measuring device set was lifted and its weight Wb (g) was measured. This weight measurement must be performed as quickly as possible and without vibrations. And the absorption capacity | capacitance under pressure (AAP) (g / g) was computed from Wa and Wb by following Formula.

AAP (g / g) = [Wb (g) -Wa (g)] / weight of water-absorbing agent (g)
<(E) FSR>
Measurement was performed with physiological saline according to US Pat.

<(F) Soluble content>
According to WO2005-92956, it measured with the physiological saline.

<(G) Moisture content>
The water content of the water-absorbing agent (or water-absorbent resin particles) was determined from loss on drying as follows.

  The water absorbent W (g) (about 2.00 g) was spread on an aluminum cup having a bottom diameter of 52 mm, and the total mass W6 (g) of the water absorbent (or water absorbent resin particles) and the aluminum cup was measured. Thereafter, the aluminum cup in which the water-absorbing agent (or the water-absorbing resin particles) was spread was dried for 3 hours with a stationary dryer having an atmospheric temperature of 180 ° C. After taking out the said aluminum cup from a dryer, it left still for 5 minutes in the desiccator of room temperature (25 degreeC +/- 2 degreeC), and the water absorbing agent (or water absorbing resin particle) was naturally cooled. Thereafter, the total mass W7 (g) of the water-absorbing agent (or water-absorbing resin particles) after drying and the aluminum cup was measured. And according to the following formula from the said W, W6, W7, the moisture content (mass%) was calculated | required.

Water content (mass%) = {(W6 (g) −W7 (g)) / W (g)} × 100
<(H) Bulk specific gravity>
The measurement was performed according to US Pat. No. 6,562,879.

Example 1
Polyethylene glycol diacrylate (a monomer concentration of 35% by mass) was added to 334 g of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid, a sodium acrylate aqueous solution, and deionized water. An average added mole number of ethylene oxide 9) 0.4 g and hydroxyethyl cellulose SP850 (manufactured by Daicel Chemical Industries) 5.0 g were dissolved to obtain an aqueous monomer solution.

  780 g of cyclohexane was placed in a 4-liter separable flask having a capacity of 2 liters equipped with a stirrer, reflux condenser, thermometer, nitrogen gas inlet tube and water bath, and sucrose fatty acid ester F-50 (Daiichi Kogyo Seiyaku Co., Ltd.) Made, HLB = 6) 4.0g was added, and it was made to disperse | distribute by stirring at 240 rpm. After the flask was purged with nitrogen, the temperature was raised to 70 ° C. The monomer aqueous solution prepared above was added thereto. After the addition, reverse phase suspension polymerization started, and after 15 minutes, the polymerization reaction peak temperature reached 74 ° C. After the peak, the temperature of the water bath was maintained at 70 ° C. for 30 minutes, the temperature of the water bath was set to 90 ° C., and dehydration was performed until the water content of the resin particles generated by azeotropy with cyclohexane was 30%.

  When the stirring was stopped after the completion of the dehydration, the resin particles settled on the bottom of the flask and were separated by decantation. The obtained resin particles are spread in a stainless steel container, heated in a hot air dryer at 150 ° C. for 2 hours, and the adsorbed cyclohexane and some water are removed to remove spherical water-absorbent resin particles (a1) Got.

  3.0 mass parts of 1st surface crosslinking agent aqueous solution which consists of 0.5 mass parts of propylene glycol, 0.3 mass part of 1, 4- butanediol, and 2.7 mass parts of water in 100 mass parts of water absorbent resin particles (a1). The water-absorbent resin particles (b1) were obtained by spray-mixing the parts and heat-treating in a hot air dryer at 180 ° C. for 1 hour. Thereafter, 1.22 parts by mass of a second surface cross-linking agent aqueous solution consisting of 0.5 parts by mass of aluminum sulfate and 0.6 parts by mass of water is further sprayed and mixed with 100 parts by mass of the water-absorbent resin particles (b1), followed by hot air drying. A spherical water-absorbing agent (Ex1) was obtained by heat treatment at 60 ° C. for 1 hour in the vessel. Various physical properties of the water-absorbing agent (Ex1) were measured, and the results are shown in Tables 1 to 3.

(Comparative Example 1)
To 5460 parts by mass (monomer concentration: 39% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 75 mol% obtained by mixing acrylic acid, an aqueous sodium acrylate solution, and deionized water, A reaction solution was prepared by dissolving 8.25 parts by mass of acrylate (average number of moles of ethylene oxide added 9). Next, the above reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma-shaped blades, and nitrogen gas was maintained while maintaining the reaction solution at 25 ° C. Dissolved oxygen was removed from the reaction solution.

  Subsequently, while stirring the reaction solution, 29.0 parts by mass of a 10% by mass aqueous solution of sodium persulfate and 4.4 parts by mass of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started after about 1 minute. did. A polymerization peak temperature of 92 ° C. was exhibited 15 minutes after the start of the polymerization, and a hydrogel polymer was taken out 40 minutes after the start of the polymerization. The obtained hydrogel polymer was fragmented into particles of about 1 to 4 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried with hot air at 180 ° C. for 40 minutes. Next, the dried product was pulverized using a roll mill, and further classified with a wire mesh having an opening of 850 μm and 150 μm to obtain irregularly crushed water-absorbent resin particles (Ca1). The absorption capacity without load (CRC) of the obtained water-absorbent resin particles (Ca1) was 33 g / g. In addition, Tables 1 and 2 show the particle size distribution of the water-absorbing resin particles (Ca1) obtained.

  100 mass parts of water-absorbent resin particles (Ca1), 3.5 mass parts of a first surface cross-linking agent aqueous solution consisting of 0.5 mass parts of propylene glycol, 0.3 mass parts of 1,4-butanediol, and 2.7 mass parts of water. The water-absorbent resin particles (C-Ex1) were obtained by spray-mixing the parts and heat-treating at 180 ° C. for 1 hour in a hot air dryer.

  The obtained water-absorbent resin particles were used as the comparative water-absorbing agent (C-Ex1) of the present invention, various physical properties were measured, and the results are shown in Tables 1 to 3.

(Comparative Example 2)
To 100 parts by mass of the water-absorbent resin particles (C-Ex1) obtained in Comparative Example 1, 1.22 parts by mass of a second surface cross-linking agent aqueous solution composed of 0.5 parts by mass of aluminum sulfate and 0.6 parts by mass of water is sprayed. By mixing and heat-treating at 60 ° C. for 1 hour in a hot air dryer, water absorbent resin particles (C-Ex2) were obtained.

  The obtained water-absorbing resin particles were used as a comparative water-absorbing agent (C-Ex2), various physical properties were measured, and the results are shown in Tables 1 to 3.

(Comparative Example 3)
To 100 parts by mass of the water-absorbent resin particles (C-Ex1) obtained in Comparative Example 1, 0.5 part by mass of Aerosil (registered trademark) 200 (manufactured by Nippon Aerosil Co., Ltd.) was dry blended, and the resulting mixture was further mixed A comparative water-absorbing agent (C-Ex3) of the present invention was obtained by passing through a sieve having an aperture of 850 μm. Various physical properties of the comparative water-absorbing agent (C-Ex3) were measured, and the results are shown in Tables 1 to 3.

(Comparative Example 4)
To 100 parts by mass of the water-absorbent resin particles (C-Ex2) obtained in Comparative Example 2, 0.5 part by mass of Aerosil (registered trademark) 200 (manufactured by Nippon Aerosil Co., Ltd.) was dry blended, and the resulting mixture was further mixed A comparative water-absorbing agent (C-Ex4) was obtained by passing through a sieve having an aperture of 850 μm.

  Various physical properties of the comparative water-absorbing agent (C-Ex4) were measured, and the results are shown in Tables 1 to 3.

(Comparative Example 5)
Polyethylene glycol diethylene glycol was added to 5452 parts by mass (monomer concentration: 41% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 71 mol% obtained by mixing acrylic acid, an aqueous sodium acrylate solution, and deionized water. 12.0 parts by mass of acrylate (average added mole number of ethylene oxide 9) was dissolved to obtain a reaction solution. Next, the above reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma-shaped blades, and nitrogen gas was maintained while maintaining the reaction solution at 25 ° C. Dissolved oxygen was removed from the reaction solution.

  Subsequently, while stirring the reaction solution, 31 parts by mass of a 10% by mass aqueous solution of sodium persulfate and 4.6 parts by mass of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. A polymerization peak temperature of 92 ° C. was exhibited 15 minutes after the start of the polymerization, and a hydrogel polymer was taken out 40 minutes after the start of the polymerization. The obtained hydrogel polymer was fragmented into particles of about 1 to 4 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried with hot air at 180 ° C. for 45 minutes. Next, the dried product was pulverized using a roll mill, and further classified with a wire mesh having openings of 710 μm and 150 μm to obtain irregularly crushed water absorbent resin particles (Ca5). The absorption capacity without load (CRC) of the obtained water-absorbent resin particles (Ca5) was 32 g / g.

  3.9 parts by mass of a first surface cross-linking agent aqueous solution consisting of 0.6 parts by mass of propylene glycol, 0.3 parts by mass of 1,4-butanediol, and 3.0 parts by mass of water to 100 parts by mass of water absorbent resin particles (Ca5). The water-absorbent resin particles (Cb5) were obtained by spray-mixing the parts and heat-treating at 180 ° C. for 1 hour in a hot air dryer. Thereafter, 1.22 parts by mass of a second surface cross-linking agent aqueous solution consisting of 0.5 parts by mass of aluminum sulfate and 0.6 parts by mass of water is further sprayed and mixed with 100 parts by mass of the water-absorbent resin particles (Cb5), followed by hot air drying. The comparative water-absorbing agent (C-Ex5) of the present invention was obtained by heat treatment at 60 ° C. for 1 hour in the vessel.

  Various physical properties of the comparative water-absorbing agent (C-Ex5) were measured, and the results are shown in Tables 1 to 3.

(Comparative Example 6)
An Erlenmeyer flask with an internal volume of 500 mL was charged with 92 g (1.02 mol) of an 80% by mass acrylic acid aqueous solution, and 146.0 g of a 21.0% by mass aqueous sodium hydroxide solution was added dropwise with ice cooling to add 75 mol% acrylic. Acid neutralization was performed to prepare a partially neutralized acrylic acid salt solution with a monomer concentration of 38% by mass.

  To the resulting partially neutralized acrylic acid aqueous solution, 9.2 mg (53 μmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent and 92 mg (0.34 mmol) of potassium persulfate as a radical polymerization initiator were added. The monomer aqueous solution (A) for the first stage polymerization was used.

  On the other hand, in a 5-liter cylindrical round bottom flask having an internal volume of 2 liters equipped with a stirrer, a two-stage paddle blade, a reflux condenser, a dropping funnel and a nitrogen gas introduction tube, 340 g (500 mL) of n-heptane and a surfactant After adding 0.92 g of sucrose fatty acid ester (HLB value 3.0) and dissolving in n-heptane, the internal temperature was set to 35 ° C. Thereafter, the monomer aqueous solution (A) for the first stage polymerization is added and maintained at 35 ° C., suspended under stirring, and the inside of the system is replaced with nitrogen gas. The first stage reverse phase suspension polymerization was performed.

  Next, separately from this, 92 g (1.02 mol) of an 80% by mass acrylic acid aqueous solution was placed in a 500 mL Erlenmeyer flask, and 146.0 g of a 21.0% by mass sodium hydroxide aqueous solution was added dropwise while cooling with ice. Then, 75 mol% of acrylic acid was neutralized to prepare a partially neutralized aqueous solution of acrylic acid having a monomer concentration of 38% by mass. To the obtained partially neutralized acrylic acid aqueous solution, 9.2 mg (53 μmol) of ethylene glycol diglycidyl ether as an internal crosslinking agent and 92 mg (0.34 mmol) of potassium persulfate as a radical polymerization initiator were added. It was set as the monomer aqueous solution (B) for reverse phase suspension polymerization of the 2nd step.

  After completion of the first-stage reversed-phase suspension polymerization, the polymerization slurry is cooled to 23 ° C., and the surfactant is precipitated, and the second-stage reversed-phase suspension polymerization monomer aqueous solution is used. (B) was dropped into the system and stirred for 30 minutes while maintaining at 23 ° C. At the same time, the inside of the system was sufficiently replaced with nitrogen gas. Polymerization was performed.

  After the reverse phase suspension polymerization was completed, 250 g of water was extracted from the azeotropic mixture of n-heptane and water by heating again, and then 368 mg (2.11 mmol) of ethylene glycol diglycidyl ether as a post-crosslinking agent. And a post-crosslinking reaction was performed in the presence of 45 g of water at 80 ° C. for 2 hours. After the cross-linking reaction, n-heptane and water in the system are distilled off by heating to obtain water-absorbing resin particles (C-Ex6) of spherical granulated particles (granulated particles composed of spherical particles, tuft-like shape). It was.

(Comparative Example 7)
To 100 parts by mass of the water-absorbent resin particles (C-Ex6) obtained in Comparative Example 6, 0.8 parts by mass of propylene glycol, 0.5 parts by mass of 1,4-butanediol, and 4.0 parts by mass of water. 1 part surface crosslinking agent aqueous solution 5.3 mass parts was spray-mixed, and the water-absorbent resin particle | grains were obtained by heat-processing in 185 degreeC for 2 hours in a hot air dryer.

  The obtained water-absorbing resin particles were used as a comparative water-absorbing agent (C-Ex7) of the present invention, various physical properties were measured, and the results are shown in Tables 1 to 3.

(Example 2)
To 100 parts by mass of the water-absorbent resin particles (C-Ex7) obtained in Comparative Example 7, 1.22 parts by mass of a second surface cross-linking agent aqueous solution composed of 0.5 parts by mass of aluminum sulfate and 0.6 parts by mass of water is sprayed. The mixture was heat-treated at 60 ° C. for 1 hour in a hot air dryer to obtain a water-absorbing agent (Ex2) of spherical granulated particles. Various physical properties of the water-absorbing agent (Ex2) were measured, and the results are shown in Tables 1 to 3. In addition, the absorption rate (FSR) of the water absorbing agent (Ex2) was 0.46 g / g / s.

( Comparative Example 8 )
Polyethylene glycol diethylene glycol was added to 5452 parts by mass (monomer concentration: 41% by mass) of an aqueous solution of sodium acrylate having a neutralization rate of 71 mol% obtained by mixing acrylic acid, an aqueous sodium acrylate solution, and deionized water. 12.0 parts by mass of acrylate (average added mole number of ethylene oxide 9) was dissolved to obtain a reaction solution. Next, the above reaction solution was supplied to a reactor formed by attaching a lid to a stainless steel double-armed kneader with an internal volume of 10 L having two sigma-shaped blades, and nitrogen gas was maintained while maintaining the reaction solution at 25 ° C. Dissolved oxygen was removed from the reaction solution.

  Subsequently, while stirring the reaction solution, 31 parts by mass of a 10% by mass aqueous solution of sodium persulfate and 4.6 parts by mass of a 1% by mass aqueous solution of L-ascorbic acid were added, and polymerization started about 1 minute later. A polymerization peak temperature of 92 ° C. was exhibited 15 minutes after the start of the polymerization, and a hydrogel polymer was taken out 40 minutes after the start of the polymerization. The obtained hydrogel polymer was fragmented into particles of about 1 to 4 mm. This finely divided hydrogel polymer was spread on a 50 mesh (mesh size 300 μm) wire net and dried with hot air at 180 ° C. for 45 minutes. Next, the dried product was pulverized using a roll mill, and further classified with a wire mesh having an opening of 850 μm and 300 μm to obtain irregularly crushed water-absorbent resin particles.

  100 g of the obtained water-absorbent resin particles were put into a homogenizer (manufactured by Nippon Seiki Co., Ltd., high-speed homogenizer, Model: MX-7), and polished at a rotational speed of 6,000 rpm for 5 minutes. The obtained water-absorbing resin particles were classified with a wire mesh having an opening of 850 μm and 300 μm, thereby obtaining polished water-absorbing resin particles.

100 parts by mass of the polished water-absorbing resin particles, 3.5 parts by mass of a first surface cross-linking agent aqueous solution consisting of 0.5 parts by mass of propylene glycol, 0.3 parts by mass of 1,4-butanediol, and 2.7 parts by mass of water. The water-absorbent resin particles were obtained by spray-mixing the part and heat-treating at 180 ° C. for 1 hour in a hot air dryer. Thereafter, 1.2 parts by mass of a second surface cross-linking agent aqueous solution consisting of 0.5 parts by mass of aluminum sulfate and 0.6 parts by mass of water is further sprayed and mixed with 100 parts by mass of the water-absorbent resin particles, and 60 parts in a hot air dryer. By carrying out heat treatment at 0 ° C. for 1 hour, the indefinitely crushed water-absorbing agent ( C-Ex8 ) of the present invention was obtained.

Various physical properties of the water-absorbing agent ( C-Ex8 ) were measured, and the results are shown in Tables 1 to 3.

  When the particulate water-absorbing agent obtained according to the present invention is used in a thin absorbent body such as a diaper at a high concentration, it provides an absorbent body that is superior in absorption performance, in particular, liquid passing characteristics, compared to conventional absorbent bodies. There is an effect that can be done.

It is general | schematic sectional drawing of the measuring apparatus used for a measurement of AAP. It is general | schematic sectional drawing of the measuring apparatus used for the measurement of the gap radius index under pressure. It is a bottom sectional view of a piston.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Plastic support cylinder 101 Stainless steel 400 mesh wire mesh 102 Water absorbing resin 103 Piston 104 Load (weight)
105 Petri dish 106 Glass filter 107 Filter paper 108 Saline 201 Filter funnel 202 Glass filter particle number # 3; Average pore size 20-30 μm 203 Conduit 204 Liquid tank 205 Clamp 206 Saline (0.9 wt% sodium chloride aqueous solution)
207 Balance 208 Automatic elevator 209 Measurement sample 210 Computer 211 Piston 212 Weight

Claims (11)

A water-absorbing agent obtained by polymerizing a water-soluble ethylenically unsaturated monomer and essentially comprising a water-absorbing resin particle having a crosslinked structure therein, wherein the water-absorbing agent has an average gap radius index of 140 or more under pressure; Including an average gap radius index improver under pressure which is a water-soluble aluminum salt,
The water-soluble aluminum salt is at least one of aluminum sulfate, potassium alum, ammonium alum, sodium alum, and (poly) aluminum chloride;
A water-absorbing agent in which the water-absorbent resin particles are spherical and the surface thereof is cross-linked.
However, the average gap radius index under pressure is a value (d50) of the swollen gel gap radius corresponding to 50% of the cumulative gap water amount ratio in physiological saline at a load of 2.07 kPa.   The water-absorbing agent according to claim 1, wherein the water-absorbing agent is obtained by reverse-phase suspension polymerization, and 90% by weight or more of the water-absorbing agent obtained by reverse-phase suspension polymerization has a particle diameter in the range of 150 to 850 µm.   The water-absorbing agent according to claim 1 or 2, wherein the water-absorbing agent has a particle shape, and an absorption capacity under load (AAP) at 4.83 kPa is 10 g / g or more.   The mass average particle diameter (D50) is 200 to 500 μm, the logarithmic standard deviation (σζ) of particle size distribution is 0.25 to 0.45, and the bulk specific gravity (g / ml) is 0.72 to 1.00. The water-absorbing agent according to any one of 1 to 3.   Absorption capacity under pressure (AAP) at 4.83 kPa is 20 g / g to 29 g / g, difference between absorption capacity under load without load (CRC) and absorption capacity under pressure (AAP) at 4.83 kPa is 7 g / g or less The water-absorbing agent according to any one of claims 1 to 4.   The water absorbing agent according to any one of claims 1 to 5, which is a granulated product. A step of crosslinking polymerization of an unsaturated monomer aqueous solution containing acrylic acid and / or a salt thereof as a main component in a hydrophobic organic solvent by reverse phase suspension polymerization, a drying step, a surface crosslinking treatment step, and was observed including the step of adding pressurized void average radius index improver is water-soluble aluminum salt to the water-absorbent resin particles of spherical, the water-soluble aluminum salt is aluminum sulfate, potassium alum, ammonium alum, sodium alum A method for producing a water-absorbing agent having an average gap radius index under pressure of 140 or more, characterized in that it is at least one of (poly) aluminum chloride .
However, the average gap radius index under pressure is a value (d50) of the swollen gel gap radius corresponding to 50% of the cumulative gap water amount ratio in physiological saline at a load of 2.07 kPa.   The production method according to claim 7, wherein 90% by weight or more of the water-absorbent resin particles are in a range of a particle diameter of 150 to 850 μm.   The internal cross-linking agent is a combination of a polymerizable cross-linking agent having two or more polymerizable unsaturated groups and a reactive internal cross-linking agent having two or more covalent bond groups or ionic bond groups. 9. The production method according to 7 or 8. The water absorbent resin particles at the time of the surface crosslinking treatment step or after the surface crosslinking are adjusted to water absorbent resin particles satisfying the following (a) to (c): The production method according to item.
(A) Mass average particle diameter (D50) is 200 to 500 μm
(B) Logarithmic standard deviation (σζ) of particle size distribution is 0.25 to 0.45
(C) Bulk specific gravity (g / ml) is 0.72-1.00   An absorbent article for absorbing urine, feces or blood, comprising the water-absorbing agent according to any one of claims 1 to 6.

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